The invention is in the field of thermal wave imaging/sensing and characterization for nondestructive/noncontact evaluation. Specifically, the invention comprises the use of microwave heating with Time Resolved Infrared Radiometry (TRIR) methods.
TRIR is a thermal characterization technique developed for the nondestructive evaluation of layered materials. In TRIR a region close to a sample's surface is heated by a source, e.g., a laser or flashlamp, with a long pulse and the sample's surface temperature is monitored as a function of time through changes in emitted infrared radiation. Specimen features which influence the production or transport of heat cause the surface temperature to change relative to areas without such features. This has allowed subsurface delaminations to be imaged.
An infrared imaging camera allows rapid, quantitative inspection at relatively high spatial resolution. However, the visibility of the subsurface specimen features in the thermal image is determined by the magnitude of the reflected thermal signal which is determined by the depth of the defect and the ratio of the thermal effusivities of region and sample. For example, for subsurface voids filled with water this contrast is small.